I am losing the format of a column when I ...

I'm using 365 On a Mac after upgrading from 2011. Lots of new things to ferret out here.

I am losing the format of a column when I do the following:

Setup:
Columns A and D are formatted as General.
I have a table of 18 names in Col A

Column D1 points to A1
Column D2 points to D2
Column D3 points to D3
etc. ...
By pointing each cell to the previous row, a cascading list of contents is created Column D1, i.e, the selection in A1 is propagated. This column D has 100 rows.

To change Column D, I double-click D1 and change =A1 to =A2 and a new cascading list of A2 is created.

Works great so far.

From here it goes pear-shape.

Alternately, I should be able to click on D1 to select a cell (i.e., currently points to =A1) and drag it down Column A to my next selection. When I do this, Column D turns all cells to a cascaded list of formula =A2.

I cannot undo this action. I feel that alternate is a preferred method vs altering a formula.

To recover, I again set up Column D1 to =A1. Forgetting that the rest of Column D is zapped, I dragged down 20 rows ending with a copy of Column A and "empty" rows of 19 and 20 with a zero on the left side of each cell. This is telltale in 19 and 20 in that the format is gone as a numeric value should be rightmost in the cells.

To confirm, I select Column D and call up Format Cells which shows the General setting is not set.

The preferred method above worked in Office for Mac 2011.
Are there any settings (Preferences in Mac: Options in Windows) that I should use to defeat this behavior?

Thx Mike